1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a sealant pattern of an LCD device.
2. Discussion of the Related Art
Generally, ultra thin flat panel displays having a display screen with a thickness of several centimeters or less, and in particular, flat panel LCD devices, are widely used in monitors for notebook computers, spacecraft, and aircraft in view of the aspects that such LCD devices have low power consumption and are easy to carry.
Such an LCD device, as shown in FIG. 1, includes a lower substrate 1, an upper substrate 3, and a liquid crystal layer 5. A thin film transistor (TFT) (not shown) and a pixel electrode (not shown) are formed on the lower substrate 1. The upper substrate 3 is formed to oppose the lower substrate 1. A light-shielding layer (not shown), a color filter layer (not shown), and a common electrode (not shown) are formed on the upper substrate 3. The liquid crystal layer 5 is formed between the lower and upper substrates 1 and 3.
A sealant 7 is formed between the lower and upper substrates 1 and 3 to prevent the liquid crystal layer 5 from leaking out.
In the aforementioned LCD device, to form the liquid crystal layer 5 between lower and upper substrates 1 and 3, a vacuum injection method based on capillary phenomenon and pressure difference has been conventionally used. However, such a vacuum injection method has a problem in that it takes long time to inject the liquid crystal over a large panel area, thereby reducing the productivity.
To solve such a problem, a method of applying liquid crystal to one of the substrates has been supposed.
A method of manufacturing an LCD device based on a liquid crystal dropping method will now be described with reference to FIGS. 2A to 2D.
As shown in FIG. 2A, a lower substrate 1 and an upper substrate 3 are prepared. A plurality of gate and data lines (not shown) are formed on the lower substrate 1. The gate lines cross the data lines to define a pixel region. A thin film transistor (not shown) is formed at each crossing point between the gate and data lines. A pixel electrode (not shown) connected with the thin film transistor is formed in the pixel region.
A light-shielding layer (not shown) is formed on the upper substrate 3 to prevent light from leaking out from the gate and data lines and the thin film transistor. Color filter layers of red(R), green(G), and blue(B) are formed on the light-shielding layer, and a common electrode (not shown) is formed on the color filter layers. An alignment film (not shown) is formed on at least one of the lower substrate 1 and the upper substrate 3 to initially align a liquid crystal.
As shown in FIG. 2B, a sealant 7 is formed on the lower substrate 1 and a liquid crystal 5 is dropped thereon, so that a liquid crystal layer is formed. A spacer (not shown) is spread or sprayed onto the upper substrate 3 to maintain a cell gap.
In the method of manufacturing the LCD device based on the liquid crystal application method, a liquid crystal layer is formed on bonded substrates. Therefore, if a thermo-hardening sealant is used as the sealant 7, the sealant 7 heats and expands and flows out of the substrate when it is heated. For this reason, a problem arises in that the liquid crystal 5 is contaminated.
Therefore, in the method of manufacturing the LCD based on the liquid crystal application method, a UV sealant is used as the sealant 7.
As shown in FIG. 2C, the lower substrate 1 is attached to the upper substrate 3.
As shown in FIG. 2D, UV is irradiated through a UV irradiating device 9 so that the sealant 7 is hardened, thereby bonding the lower substrate 1 to the upper substrate 3.
Thereafter, although not shown, a cell cutting process and a final test process are performed.
The aforementioned liquid crystal dropping method has an advantage in that it takes a short time to form the liquid crystal layer as compared with the vacuum injection method because the liquid crystal 5 is directly applied onto the lower substrate 1 before the substrates 1 and 3 are bonded to each other. However, the liquid crystal application method has the following problems.
First, although an amount of the liquid crystal dropped onto the substrate is generally determined considering some factors such as the size of the substrate and a cell gap between both substrates, it is difficult to exactly determine the amount of the liquid crystal applied on the substrate.
Accordingly, if the liquid crystal is applied in an amount less than the required amount, regions of the substrate where the liquid crystal is filled imperfectly, particularly, occur at four corners located farthest from the center of the substrate. If the liquid crystal is dropped excessively, a partial region where the liquid crystal is filled excessively occurs.
This deteriorates uniformity of the cell gap and picture characteristics.
Even if the liquid crystal is applied appropriately, it takes a certain time to spread the liquid crystal from the center part of the substrate to the corners. Accordingly, if the imperfectly filled region occurs as the liquid crystal is not spread to the corner regions before a final test process, the final test process cannot be carried out.
Finally, if the substrate is heated during the process of manufacturing an LCD device, the liquid crystal expands. In this case, a partial region where the liquid crystal is filled excessively also occurs, thereby reducing uniformity of a cell gap.